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Published February 21, 2017 | Submitted + Published
Journal Article Open

Hierarchical star formation across the grand-design spiral NGC 1566

Abstract

We investigate how star formation is spatially organized in the grand-design spiral NGC 1566 from deep Hubble Space Telescope photometry with the Legacy ExtraGalactic UV Survey. Our contour-based clustering analysis reveals 890 distinct stellar conglomerations at various levels of significance. These star-forming complexes are organized in a hierarchical fashion with the larger congregations consisting of smaller structures, which themselves fragment into even smaller and more compact stellar groupings. Their size distribution, covering a wide range in length-scales, shows a power law as expected from scale-free processes. We explain this shape with a simple 'fragmentation and enrichment' model. The hierarchical morphology of the complexes is confirmed by their mass–size relation that can be represented by a power law with a fractional exponent, analogous to that determined for fractal molecular clouds. The surface stellar density distribution of the complexes shows a lognormal shape similar to that for supersonic non-gravitating turbulent gas. Between 50 and 65 per cent of the recently formed stars, as well as about 90 per cent of the young star clusters, are found inside the stellar complexes, located along the spiral arms. We find an age difference between young stars inside the complexes and those in their direct vicinity in the arms of at least 10 Myr. This time-scale may relate to the minimum time for stellar evaporation, although we cannot exclude the in situ formation of stars. As expected, star formation preferentially occurs in spiral arms. Our findings reveal turbulent-driven hierarchical star formation along the arms of a grand-design galaxy.

Additional Information

© 2017 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. Received 11 January 2017; revision received 09 February 2017; accepted 17 February 2017; published 21 February 2017. DAG kindly acknowledges financial support by the German Research Foundation (DFG) through programme GO 1659/3-2. He would also like to thank S. Hony for the long discussions (and debates) on star formation and the derived MF. This research has made use of the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. This research has also made use of the SIMBAD data base (Wenger et al. 2000), operated at CDS, Strasbourg, France. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the data archive at the Space Telescope Science Institute (STScI). STScI is operated by the Association of Universities for Research in Astronomy, Inc. under NASA contract NAS 5-26555. These observations are associated with programme GO-13364. Support for programme 13364 was provided by NASA through grants from STScI. This research made use of the topcat application (Taylor 2005), the r environment for statistical computing and graphics (R Core Team 2015) and NASA Astrophysics Data System (ADS) bibliographic services.

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August 22, 2023
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